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Re: Combining InterpolatingFunctions

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  • Subject: [mg107125] Re: Combining InterpolatingFunctions
  • From: Bill Rowe <readnews at>
  • Date: Wed, 3 Feb 2010 06:11:40 -0500 (EST)

On 2/2/10 at 3:30 AM, Simon.Pearce at (Simon Pearce)

>I have two sets of InterpolatingFunctions coming from two separate
>NDSolve's. One of them is defined over the region [0,rc] and the
>other over the region [rc,2]. I would like Mathematica to
>automatically choose the correct one when I use a replacement rule.
>If I could tell it never to extrapolate this would be perfect,
>though I don't seem to be able to.

>Can anyone suggest an efficient way of combining
>InterpolatingFunctions without re-interpolating them? Or turning the
>extrapolation off!

Use Piecewise to construct a new function that combines the two
InterpolatingFunctions returned. Something like

f[x_]:=Piecewise[{{u[x], 0<x<rc}, {y[x], rc<x<2}}]

where u,v are the two interpolating functions you want to
combine. When combined as above outside the range of 0 to 2, f
is not defined. So, no extrapolation will be done.

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